Battery assembly with linear bus bar configuration

ABSTRACT

A battery assembly utilizing a compact and robust bus bar configuration is provided. The batteries within the assembly are divided into groups, where the batteries within each battery group are connected in parallel and the groups are connected in series. The batteries are interconnected using a repetitive sequence of non-overlapping, alternating polarity bus bars. The bus bars, which are integrated into a battery assembly upper tray member, are devoid of contact fingers and positioned such that there is a single bus bar located adjacent to either side of each battery group.

FIELD OF THE INVENTION

The present invention relates generally to battery packs and, moreparticularly, to a robust and compact design for a battery assembly busbar configuration.

BACKGROUND OF THE INVENTION

A bus bar is a metal strip or bar that conducts electricity and is usedfor electrical power distribution. Battery cells can be connected withbus bars to make battery packs. Some battery packs using cylindricalcells make electrical connections to the tops and the bottoms of thecells. When connecting cells in series, bus bars and high currentinterconnects link the positive terminal of one cell, or a parallelgroup of cells, to the negative terminal of the next cell or the nextparallel group of cells. Unfortunately, connections to the bottoms ofthe cells may prevent the efficient operation of either an air-based ora liquid coolant-based cooling system that is being used to remove theheat generated by the cells during operation. In addition, the highcurrent interconnect from the bottoms of the cells to the bus bars,which may be in the form of a wire somewhat longer than the length ofthe cell, introduces a small amount of resistance which gives rise to avoltage drop at high current levels. Furthermore, assembly of this wireto the bus bars and/or to the bottom of each of the batteries adds tothe manufacturing cost of the battery pack while potentially introducingreliability issues.

Accordingly, what is needed is a robust bus bar configuration thatallows the efficient assembly of a battery pack system while notaffecting operation of the battery pack thermal management system. Thepresent invention provides such a bus bar design.

SUMMARY OF THE INVENTION

The present invention provides a battery assembly comprised of (i) aplurality of batteries where each battery includes both a first terminaland a second terminal accessible at a first end portion of the battery,where the plurality of batteries are divided into a plurality of batterygroups with each battery group comprised of a subset of the batteries,where the batteries within each subset are electrically connected inparallel, and where the battery groups are electrically connected inseries; (ii) an upper tray member, where the upper tray member capturesthe first end portion of each battery, and where the upper tray memberincludes a plurality of apertures that provide access to the first andsecond battery terminals of each battery; and (iii) a plurality of busbars attached to an upper surface of the upper tray member, where theplurality of bus bars are non-overlapping, devoid of contact fingers,and configured in an alternating pattern with the plurality of batterygroups, where the alternating pattern alternates a single bus bar with asingle battery group such that only one bus bar is adjacent to eitherside of each battery group, where a first set of the bus bars are of afirst polarity and a second set of the bus bars are of a secondpolarity, where the plurality of bus bars attached to the upper surfaceof the upper tray member alternate between the first polarity and thesecond polarity, where each battery of a corresponding battery group iselectrically connected via the first terminal to one bus bar of thefirst set of bus bars adjacent to a first side of the correspondingbattery group and electrically connected via the second terminal to onebus bar of the second set of bus bars adjacent to a second side of thecorresponding battery group. Preferably the bus bars are linear and ofapproximately uniform thickness and of approximately uniform width. Theupper surface of each bus bar may be coplanar with the upper surface ofthe upper tray member. The bus bars may be molded into, or bondeddirectly to, the upper surface of the upper tray member. The pluralityof apertures corresponding to the upper tray member may be comprised ofa single aperture per battery group, where the single aperture providesaccess to the first and second terminals of each battery of thecorresponding battery group. Wire bonds may be used to electricallyconnect the batteries to the bus bars, where the wire bonds may utilizea bonding technique selected from the group consisting of ultrasonicbonding, resistance bonding, thermocompression bonding and thermosonicbonding.

In one aspect, the assembly may further include a lower tray member thatincludes a second plurality of apertures and which captures a second endportion of each battery. A heat spreader (e.g., a metal heat spreaderwith a thermal conductivity of at least 100 Wm⁻¹K⁻¹) may be coupled to alower surface of the lower tray member such that a lowermost surface ofeach battery passes through the lower tray member and thermally contactsan upper surface of the heat spreader. A thermally conductive material(e.g., a material with a thermal conductivity of at least 2.0 Wm⁻¹K⁻¹and an electrical resistivity of at least 10¹² ohm-cm) may be interposedbetween the upper surface of the heat spreader and the lowermost surfaceof each battery. A heat sink or a thermal management system comprised ofat least one cooling conduit may be in thermal contact with a lowersurface of the heat spreader. The assembly may further include a batteryseparating member that includes a plurality of six-sided cavities thatcorrespond to the plurality of batteries, where the first end portion ofeach battery extends out of a first side of the battery separatingmember and is captured by the upper tray member, and where the secondend portion of each battery extends out of a second side of the batteryseparating member and is captured by the lower tray member. The uppertray member, the lower tray member and the battery separating member maybe fabricated from plastic.

In another aspect, the assembly may further include a battery separatingmember that includes a plurality of six-sided cavities that correspondto the plurality of batteries, where the first end portion of eachbattery extends out of a first side of the battery separating member andis captured by the upper tray member. Each side of each six-sided cavitymay be straight and of equal length; alternately, each side of eachsix-sided cavity may curve inwards towards a corresponding cavitycenterline; alternately, each side of each six-sided cavity may curveoutwards away from a corresponding cavity centerline.

In another aspect, each of the batteries comprising the plurality ofbatteries may be cylindrical, for example utilizing an 18650 formfactor. The first terminal of each of the batteries may be comprised ofthe battery positive terminal while the second terminal of each of thebatteries may be comprised of the battery casing.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

It should be understood that the accompanying figures are only meant toillustrate, not limit, the scope of the invention and should not beconsidered to be to scale. Additionally, the same reference label ondifferent figures should be understood to refer to the same component ora component of similar functionality.

FIG. 1 provides a schematic diagram of a battery pack with bus barsabove and below the battery cells in accordance with the prior art;

FIG. 2 provides a schematic diagram of a battery pack with both bus barsadjacent to one end of each of the battery cells in accordance with theprior art;

FIG. 3 provides a detailed perspective view of the bus bars in aparticular layer stack configuration in accordance with the prior art;

FIG. 4 provides a simplified view of a battery module in accordance withthe present invention;

FIG. 5 provides a schematic diagram of a battery pack utilizing aplurality of the battery modules shown in FIG. 4 combined in a seriesconfiguration;

FIG. 6 provides a schematic diagram of a battery pack utilizing aplurality of the battery modules shown in FIG. 4 combined in a parallelconfiguration;

FIG. 7 provides a perspective view of a portion of a battery module suchas that shown in FIG. 4;

FIG. 8 provides a simplified view of a battery module in accordance withan alternate embodiment of the invention;

FIG. 9 provides a perspective view of the same portion of the batterymodule as shown in FIG. 8, with the upper tray member as well as thebatteries removed; and

FIG. 10 provides a perspective view of the same portion of the batterymodule as shown in FIGS. 8 and 9, with the upper tray member, batteryseparating member and the batteries removed.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises”, “comprising”, “includes”, and/or“including”, as used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features, processsteps, operations, elements, components, and/or groups thereof. As usedherein, the term “and/or” and the symbol “/” are meant to include anyand all combinations of one or more of the associated listed items.Additionally, while the terms first, second, etc. may be used herein todescribe various steps, calculations or components, these steps,calculations or components should not be limited by these terms, ratherthese terms are only used to distinguish one step, calculation orcomponent from another. For example, a first calculation could be termeda second calculation, and, similarly, a first step could be termed asecond step, without departing from the scope of this disclosure.

In the following text, the terms “battery”, “cell”, and “battery cell”may be used interchangeably and may refer to any of a variety ofdifferent battery configurations and chemistries. Typical batterychemistries include, but are not limited to, lithium ion, lithium ionpolymer, nickel metal hydride, nickel cadmium, nickel hydrogen, nickelzinc, and silver zinc. The term “battery pack” as used herein refers toan assembly of batteries electrically interconnected to achieve thedesired voltage and capacity, where the battery assembly is typicallycontained within an enclosure. The terms “electric vehicle” and “EV” maybe used interchangeably and may refer to an all-electric vehicle, aplug-in hybrid vehicle, also referred to as a PHEV, or a hybrid vehicle,also referred to as a HEV, where a hybrid vehicle utilizes multiplesources of propulsion including an electric drive system.

FIG. 1 illustrates a portion of an exemplary battery pack 100 thatutilizes a common battery pack configuration. As shown, battery pack 100includes a first group of batteries 102 and 104 connected in parallel, asecond group of batteries 106 and 108 connected in parallel, and a thirdgroup of batteries 110 and 112 connected in parallel. The first, secondand third groups of batteries are connected in series. Bus bars 114,116, 118, 120, 122, 124 are used to connect the batteries in thisparallel and series arrangement. Each of the bus bars is coupled to therespective batteries with one or more interconnects 125. A relativelythick wire 126 couples the second bus bar 114 to the third bus bar 122,making a series connection between the first and second battery groups,while a second relatively thick wire 128 couples the fourth bus bar 116to the fifth bus bar 124, making a series connection between the secondand third battery groups. As a result, the first bus bar 120 is thenegative terminal while the sixth bus bar 118 is the positive terminalfor battery pack 100.

The use of bus bars at both ends of the batteries as illustrated in FIG.1 requires a relatively complex manufacturing process in order to (i)attach the battery interconnects 125 between the battery end surfacesand the bus bars, and (ii) attach the wires (e.g., wires 126 and 128)that couple the upper bus bars to the lower bus bars. Wires 126 and 128are also problematic in the sense that they can introduce parasiticresistance into the current path, which in turn can introduce a voltagedrop under high current drain conditions. Additionally thisconfiguration prevents, or at least limits, the ability to efficientlyremove battery pack heat by affixing a heat sink to a battery endsurface.

FIG. 2 illustrates a battery pack 200 utilizing an alternate batterypack configuration in which all the bus bars are proximate to one end ofthe battery pack, thus enabling efficient heat removal from the otherend of the battery pack. Furthermore, by locating bus bars 214, 216, 218and 222 proximate to one end of the batteries, fewer bus bars arerequired than in battery pack 100. The relatively thick wires 126 and128 from the upper bus bars to the lower bus bars are also eliminated inthe embodiment shown in FIG. 2.

Access to both the positive and negative terminals in battery pack 200is at one end of the cells, i.e., at the top end of the cells, where thebus bars are coupled to the positive and negative terminals usingbattery interconnects. As in the prior arrangement, the first group ofbatteries 102 and 104 are connected in parallel, the second group ofbatteries 106 and 108 are connected in parallel, and the third group ofbatteries 110 and 112 are connected in parallel. The first, second andthird groups of batteries are connected in series. Bus bars 214, 216,218, 222 are used to couple the batteries in this parallel and seriesarrangement. Specifically, starting with the negative terminal ofbattery pack 200, a first bus bar 214 is connected to the negativeterminals of the first group of batteries 102 and 104 while a second busbar 222 is connected to the positive terminals of the same group ofbatteries 102 and 104, both at the top end portion 138 of each of thebatteries. The first and second bus bars 214 and 222 couple the firstgroup of batteries 102 and 104 in parallel. Similarly, the second busbar 222 and the third bus bar 216 couple the second group of batteries106 and 108 in parallel, while the third bus bar 216 and the fourth busbar 218 couple the third group of batteries 110 and 112 in parallel.Series connections between battery groups are formed by the bus bars,specifically the second bus bar 222 connects the positive terminals ofthe first group of batteries 102 and 104 to the negative terminals ofthe second group of batteries 106 and 108; and the third bus bar 216connects the positive terminals of the second group of batteries 106 and108 to the negative terminals of the third group of batteries 110 and112. The fourth bus bar 218 is the positive terminal of the battery pack200.

In battery pack 200 the bus bars are arranged in a layer stack 250. Inthis stacking arrangement first bus bar 214 and third bus bar 216, whichare separated by an air gap or other electrical insulator to preventshort circuiting, are placed in a first layer 230. Similarly, second busbar 222 and fourth bus bar 218, which are also separated by a gap orinsulator, are placed in a third layer 234. Disposed between layers 230and 234 is an electrically insulating layer 232. To simplifyfabrication, the layer stack may be formed using layers of a circuitboard, e.g., with the bus bars made of (or on) copper layers or othersuitable conductive metal (such as aluminum) and the insulating layermade of resin impregnated fiberglass or other suitable electricallyinsulating material.

The batteries shown in FIGS. 1 and 2, as well as the batteries used inthe preferred embodiment of the invention, have a projecting nub as apositive terminal at the top end of the battery and a can, also referredto as a casing, that serves as the negative battery terminal. Thebatteries are preferably cylindrically shaped with a flat bottom surface(e.g., 18650 form factor). Typically a portion of the negative terminalis located at the top end of the cell, for example due to a casing crimpwhich is formed when the casing is sealed around the contents of thebattery. This crimp or other portion of the negative terminal at the topend of the battery provides physical and electrical access to thebattery's negative terminal. The crimp is spaced apart from theperipheral sides of the projecting nub through a gap that may or may notbe filled with an insulator.

Preferably in a battery pack such as battery pack 200 in which thebattery connections are made at one end of the cells (e.g., end portions138), a heat sink 252 is thermally coupled to the opposite end portions140 of each of the batteries. This approach is especially applicable toa co-planar battery arrangement which provides a relatively flat surfaceto attach a heat sink. Heat sink 252 may be finned or utilize air orliquid coolant passages. If heat sink 252 is air cooled, a fan may beused to provide air flow across one or more heat sink surfaces. In someconfigurations, heat sink 252 may be attached or affixed to the bottomof a battery holder.

In a typical battery pack in which all battery connections are made atone end of the cells, typically a multi-layer stack (e.g., stack 250) isused in order to provide bus bars for both terminals as well as asuitable insulator located between the bus bars. This approach resultsin a relatively complex bus bar arrangement. For example FIG. 3 fromco-assigned U.S. patent application Ser. No. 14/203,874, filed 11 Mar.2014, illustrates a multi-layer bus bar configuration in which the busbars are stacked with an interposed insulator, and in which each bus barincludes multiple contact fingers 301.

In order to simplify bus bar design and configuration, therebysignificantly reducing material and fabrication costs as well as overallbattery pack complexity, the present invention utilizes a series ofnon-overlapping, linear bus bars of alternating polarity. Although thisapproach may be used throughout the entire battery pack, preferably itis used to form battery modules, where the battery modules are thenelectrically coupled to form the battery pack. Assuming the battery packis used in an electric vehicle as preferred, the individual batterymodules may be contained within a single battery pack enclosure, orwithin multiple enclosures, the latter approach allowing subsets ofmodules to be distributed throughout the vehicle in order to obtain aparticular weight distribution or to fit within the confines of aparticular vehicle envelope or structure.

FIG. 4 provides a top view of a battery module 400 configured per theinvention. In this embodiment, the end portion of a plurality ofbatteries 401 is visible, and accessible, through correspondingapertures in an upper tray member 403. Tray member 403 is preparedand/or treated to provide electrical isolation between batteries, forexample by fabricating the tray member from an electrically insulativematerial such as a plastic, or coating the tray member with anelectrically insulative material. The batteries are divided into aplurality of rows 405, where each row 405 includes sixteen batteries401. Even though module 400 is shown with seven rows 405, it should beunderstood that the invention is not limited to configurations utilizingthis number of battery rows, and therefore is equally applicable toconfigurations utilizing a fewer number, or a greater number, of batteryrows 405. Similarly, the invention is not limited to configurations inwhich each battery row is comprised of sixteen batteries, rather theinvention may be used with configurations using a fewer number, or agreater number, of batteries 401 per battery row 405.

Interposed between battery rows 405 are linear bus bars 407, where eachbus bar 407 is devoid of the contact fingers utilized in the prior artapproach shown in FIG. 3. Bus bars 407 are preferably made of copper,although other suitable electrically conductive materials such asaluminum may be used. While the invention may utilize any battery typethat provides access to both terminals at a single end portion of thebattery, in the preferred and illustrated embodiment batteries 401 arecylindrical, preferably utilizing an 18650 form factor.

The batteries within a single row 405 form a group with all terminals ofa first polarity being electrically connected to a single bus bar on oneside of the battery row, and all terminals of the second polarity beingelectrically connected to a single bus bar on the other side of thebattery row. For example, all positive terminals of battery row 405A areelectrically connected to bus bar 407A and all negative terminals ofbattery row 405A are electrically connected to bus bar 407B. As a resultof this approach, each group of batteries represented by a single roware electrically connected in parallel while the battery rows within asingle module 400 are electrically connected in series. By varying thenumber of batteries within a single row, as well as the number of rowswithin a single module, the desired voltage and current capabilities ofthe module may be configured as desired to meet the design criteria ofthe intended application.

In the preferred embodiment of the invention, the interconnects 409 thatelectrically couple the batteries 401 to the bus bars 407 are comprisedof wire bonds. Interconnects 409 may be attached using any wire bondingtechnique suitable for the selected wire gauge, wire material and busbar material. Typical wire bonding techniques include, but are notlimited to, ultrasonic bonding, resistance bonding, thermocompressionbonding and thermosonic bonding.

As previously noted, module 400 may be configured as the entire batterypack. For some applications, however, multiple modules 400 may beelectrically interconnected in order to achieve the desired battery packoutput characteristics. For example, modules 400 may be electricallyinterconnected in series as illustrated in FIG. 5, or electricallyinterconnected in parallel as illustrated in FIG. 6. Otherseries/parallel arrangements may be used with the invention.

FIG. 7 provides a perspective view of a portion of a battery module suchas the module shown in FIG. 4. For clarity only a portion of theillustrated batteries shown in FIG. 7 are interconnected to adjacent busbars. This figure shows a clearer view of the access apertures 701fabricated into upper tray member 403, apertures 701 allowing access tothe battery terminals located at the ends of the batteries. The accessapertures 701 utilized in the illustrated embodiment are continuousslots that provide easy electrical access to all of the batteries withina single row while still holding the batteries in place. Thus in thisconfiguration there is a single access aperture per battery group. Itshould be understood, however, that access apertures 701 may utilize analternate shape and may be configured to allow access to more or lessthan a battery group. For example, the access apertures may beconfigured with a circular or elliptical shape with one opening perbattery, or one opening per sub-group of batteries (e.g., two or morebatteries).

Upper tray member 403, which may be molded, cast, printed using a 3Dprinter, or fabricated using an alternate technique, is preferablyfabricated from a plastic (e.g., polycarbonate, acrylonitrile butadienestyrene (ABS), polypropylene (PP), polyethylene (PE), polyethyleneterephthalate (PET), nylon, etc.), although other materials may also beused to fabricate the tray member. In a preferred embodiment, bus bars407 are integrated into upper tray member 403, for example by moldingthe bus bars into the tray member during tray member fabrication.Alternately, bus bars 407 may be bonded into slots molded into the uppertray member 403. Integrating the bus bars into the upper surface of traymember 403 insures that the bus bars are properly positioned during thebattery interconnection process, and that the bus bars do not move afterbattery pack fabrication as such movement would stress, and potentiallydamage, the battery interconnects. Additionally, by making the topsurfaces of the bus bar and the tray member coplanar as desired andillustrated, there is no line-of-sight between a battery terminal andthe bus bar. As a result, if a battery interconnect fuses, the risk ofarcing between the affected battery and the adjacent bus bar is reduced.

In the preferred and illustrated embodiment, bus bars 407 are linear,i.e., they are fabricated as straight bus bars and are devoid of contactfingers. As noted above, this approach simplifies module fabricationwhile reducing bus bar material, and thus cost and weight, of the pack.It will be appreciated that this configuration works best when thebattery groups, e.g., battery rows 405, are also arranged linearly. Ifthe battery groups are not arranged in a linear fashion, the bus barsmay utilize a similar shape. For example and as illustrated in FIG. 8,if each row of batteries 401 are arranged in a non-linear fashion, busbars 801 may utilize a similar curvilinear shape. In module 800, busbars 801 utilize a zig-zag shape. However, as this configuration avoidsthe use of bus bar contact fingers and instead maintains bus bars ofapproximately uniform width, a relatively simple and cost effectiveconfiguration is still achieved.

Other aspects of a preferred embodiment of the invention are also shownin FIG. 7, specifically the lower tray member 703, the batteryseparating member 705 and the heat spreader 707. These other aspects arehighlighted in FIGS. 9 and 10. It will be appreciated that theconfiguration of members 701, 703 and 705 assume the use of cylindricalcells, as preferred, and the use of an alternate form factor forbatteries 401 would require the redesign of members 701, 703 and 705.

FIG. 9 provides a clear view of the battery separating member 705.Separating member 705 is fabricated from an electrically insulatingmaterial, preferably a plastic such as a polycarbonate, acrylonitrilebutadiene styrene (ABS), polypropylene (PP), polyethylene (PE),polyethylene terephthalate (PET), or nylon. In the preferred embodiment,member 705 is fabricated using an extrusion process, although alternatefabrication techniques may be used, such as molding, casting or printingusing a 3D printer.

In the illustrated embodiment, each battery 401 is held within its owncavity 901 within separating member 705. The walls 903 of each batterycavity 901 may utilize any of a variety of shapes, such that each cavitymay have either a circular or a non-circular cross-section. In thepreferred embodiment, each battery cavity 901 is fabricated with asix-sided shape in which the six sides are of equal length (i.e., asix-sided, regular shape). Each wall 903 may be straight; alternately,each wall 903 may be curved outwardly away from the cavity center line;alternately, each wall 903 may be curved inwardly towards the cavitycenter line as shown.

Enclosing each battery within a six-sided, regular cavity, and morepreferably a six-sided, regular cavity in which the cavity walls 903curve inwardly towards the corresponding cavity center line as shown,provides several benefits. First, the cavities prevent the batteriesfrom accidentally touching one another, either during battery packfabrication and assembly or once the battery pack is installed. Assumingthat the battery pack is installed in an electric vehicle, separatingmember 705 also helps to prevent battery shorting if the battery pack isdamaged during a collision. Second, the use of a six-sided, regularcavity rather than a cavity with a circular cross-section simplifiesbattery pack assembly since the six-sided shape provides additionalfitting flexibility, thereby allowing the fabrication tolerances forboth the batteries and the separating member to be looser than wouldotherwise be required. Third, the air space provided by the six-sidedbattery cavities improves battery-to-battery thermal isolation. Fourth,the contraction and expansion that batteries often exhibit duringthermal cycling is more easily handled by a six-sided cavity rather thana circularly-shaped cavity. Fifth, the space between the corners of asix-sided cavity and a cylindrically-shaped battery provide ventingpathways if the battery vents through its side, for example during athermal runaway event.

FIG. 10 provides a view of the lower tray member 703 and heat spreader707. Tray member 703 is typically fabricated from the same electricallyinsulating material as that used for member 705, although a differentelectrically insulating material may be used. Preferably member 703 isfabricated from a plastic (e.g., polycarbonate, acrylonitrile butadienestyrene (ABS), polypropylene (PP), polyethylene (PE), polyethyleneterephthalate (PET), or nylon). Member 703 may be molded, for exampleusing injection molding, although other fabrication techniques may beused. Preferably the six-sided cavities used in battery separatingmember 705 are continued via cavities 1001 through tray member 703.Cavities 1001 pass completely through tray member 703, thereby allowinggood thermal contact to be made between batteries 401 and the underlyingthermally conductive heat spreader 707. In the preferred embodimentmember 707 is fabricated from aluminum, although it should be understoodthat spreader 707 may be fabricated from other thermally conductivematerials. Preferably heat spreader 707 has a thermal conductivity of atleast 100 Wm⁻¹K⁻¹.

In order to achieve the desired level of heat withdrawal, the lowermostsurface of each battery 401, and more preferably the lower portion ofeach battery 401, is thermally coupled to the heat spreader 707 using alayer 1003 of a thermally conductive material, for example a thermallyconductive epoxy, where the selected material preferably has a thermalconductivity of at least 0.75 Wm⁻¹K⁻¹, more preferably of at least 2.0Wm⁻¹K⁻¹, still more preferably of at least 5.0 Wm⁻¹K⁻¹, yet still morepreferably of at least 10.0 Wm⁻¹K⁻¹, and yet still more preferably of atleast 20.0 Wm⁻¹K⁻¹. Heat withdrawal from the batteries is enhanced bythermally coupling the lower portion of each battery to the heatspreader 707 via layers 1003 as preferred, rather than simplyinterposing layers 1003 between the lowermost surface of each batteryand the heat spreader. While layers 1003 are preferably comprised of athermally conductive epoxy as noted above, the inventor envisions theuse of other materials as well (e.g., a ceramic). Although not shown inthe figures, preferably heat is withdrawn from the heat spreader viaeither an air cooled heat sink or a heat transfer liquid contained in aseries of cooling conduits that are in thermal contact with thelowermost surface of heat spreader 707.

The material comprising each layer 1003 is selected to have a relativelyhigh electrical resistivity, preferably on the order of at least 10¹²ohm-cm, thus electrically isolating the batteries from the underlyingheat spreader 707. Although not required, in at least one configurationof the invention, and as described in detail in co-pending andco-assigned U.S. patent application Ser. No. 14/331,300 the disclosureof which is incorporated herein for any and all purposes, a plurality ofelectrically non-conductive granules, for example fabricated fromalumina or silica, are dispersed within layers 1003. As a result of thegranules, even if layers 1003 soften, the granules help prevent thebatteries from contacting the underlying heat spreader.

Systems and methods have been described in general terms as an aid tounderstanding details of the invention. In some instances, well-knownstructures, materials, and/or operations have not been specificallyshown or described in detail to avoid obscuring aspects of theinvention. In other instances, specific details have been given in orderto provide a thorough understanding of the invention. One skilled in therelevant art will recognize that the invention may be embodied in otherspecific forms, for example to adapt to a particular system or apparatusor situation or material or component, without departing from the spiritor essential characteristics thereof. Therefore the disclosures anddescriptions herein are intended to be illustrative, but not limiting,of the scope of the invention.

What is claimed is:
 1. A battery assembly, comprising: a plurality ofbatteries, each battery of said plurality of batteries comprising afirst terminal at a first end portion of said battery and a secondterminal at said first end portion of said battery, wherein saidplurality of batteries are divided into a plurality of battery groups,each battery group of said plurality of battery groups comprising asubset of said plurality of batteries, wherein said batteries withineach subset of said plurality of batteries are electrically connected inparallel, and wherein said battery groups of said plurality of batterygroups are electrically connected in series; an upper tray member,wherein said upper tray member captures said first end portion of eachbattery of said plurality of batteries, said upper tray member furthercomprising a plurality of apertures, wherein said plurality of aperturesprovide access to said first terminal and to said second terminal ofeach battery of said plurality of batteries; a plurality of bus barsattached to an upper surface of said upper tray member, wherein saidplurality of bus bars are non-overlapping, wherein said plurality of busbars are devoid of contact fingers, wherein said plurality of bus barsare configured in an alternating pattern with said plurality of batterygroups, wherein said alternating pattern alternates a single bus bar ofsaid plurality of bus bars with a single battery group of said pluralityof battery groups such that only one bus bar is adjacent to either sideof each battery group, wherein a first set of said bus bars are of afirst polarity and wherein a second set of said bus bars are of a secondpolarity, wherein said plurality of bus bars attached to said uppersurface of said upper tray member alternate between said first polarityand said second polarity, wherein each battery of a correspondingbattery group is electrically connected via said first terminal to onebus bar of said first set of bus bars adjacent to a first side of saidcorresponding battery group and electrically connected via said secondterminal to one bus bar of said second set of bus bars adjacent to asecond side of said corresponding battery group; a lower tray membercomprising a second plurality of apertures corresponding to saidplurality of batteries, wherein said lower tray member captures a secondend portion of each battery of said plurality of batteries; and a heatspreader coupled to a lower surface of said lower tray member, whereinat least a lowermost surface of each battery of said plurality ofbatteries passes through said lower tray member and is in thermalcontact with an upper surface of said heat spreader.
 2. The batteryassembly of claim 1, wherein said plurality of bus bars are linear andof approximately uniform thickness and of approximately uniform width.3. The battery assembly of claim 1, wherein an upper surface of each busbar of said plurality of bus bars is coplanar with said upper surface ofsaid upper tray member.
 4. The battery assembly of claim 1, wherein eachbus bar of said plurality of bus bars is molded into said upper surfaceof said upper tray member.
 5. The battery assembly of claim 1, whereineach bus bar of said plurality of bus bars is bonded to said uppersurface of said upper tray member.
 6. The battery assembly of claim 1,wherein said heat spreader is fabricated from a metal with a thermalconductivity of at least 100 Wm⁻¹K⁻¹.
 7. The battery assembly of claim1, further comprising a thermally conductive material interposed betweensaid upper surface of said heat spreader and said lowermost surface ofeach battery of said plurality of batteries.
 8. The battery assembly ofclaim 7, wherein said thermally conductive material has a thermalconductivity of at least 2.0 Wm⁻¹K⁻¹.
 9. The battery assembly of claim7, wherein said thermally conductive material has an electricalresistivity of at least 10¹² ohm-cm.
 10. The battery assembly of claim1, further comprising a heat sink thermally coupled to a lower surfaceof said heat spreader.
 11. The battery assembly of claim 1, furthercomprising a thermal management system comprising a least one coolingconduit, said at least one cooling conduit in thermal contact with alower surface of said heat spreader.
 12. The battery assembly of claim1, further comprising a battery separating member, said batteryseparating member comprising a plurality of cavities corresponding tosaid plurality of batteries, wherein said first end portion of each ofsaid plurality of batteries extends out of a first side of said batteryseparating member and is captured by said upper tray member, and whereinsaid second end portion of each of said plurality of batteries extendsout of a second side of said battery separating member and is capturedby said lower tray member, and wherein each cavity of said plurality ofcavities has six sides.
 13. The battery assembly of claim 12, whereinsaid upper tray member, said lower tray member, and said batteryseparating member are each fabricated from a plastic material.
 14. Thebattery assembly of claim 1, further comprising a battery separatingmember, said battery separating member comprising a plurality ofcavities corresponding to said plurality of batteries, wherein saidfirst end portion of each of said plurality of batteries extends out ofa first side of said battery separating member and is captured by saidupper tray member, and wherein each cavity of said plurality of cavitieshas six sides.
 15. The battery assembly of claim 14, wherein each sideof said six sides is straight, and wherein said six sides are of equallength.
 16. The battery assembly of claim 14, wherein each side of saidsix sides curves inward towards a corresponding cavity centerline. 17.The battery assembly of claim 14, wherein each side of said six sidescurves outward away from a corresponding cavity centerline.
 18. Thebattery assembly of claim 1, said plurality of apertures comprising asingle aperture per corresponding battery group, said single apertureproviding access to said first terminal and said second terminal of eachbattery of said corresponding battery group.
 19. The battery assembly ofclaim 1, wherein each of said plurality of batteries is cylindrical,wherein said first terminal is comprised of a battery positive terminal,and wherein said second terminal is comprised of a battery casing. 20.The battery assembly of claim 1, further comprising a plurality of wirebonds that electrically connect said plurality of batteries to saidplurality of bus bars.
 21. The battery assembly of claim 20, whereinsaid plurality of wire bonds are coupled to said plurality of batteriesand to said plurality of bus bars utilizing a bonding technique selectedfrom the group consisting of ultrasonic bonding, resistance bonding,thermocompression bonding and thermosonic bonding.